Пост в Trans Siberian/Mongolian train and places, Visa info, How to buy tickets, etc

Hello, I took trans-siberian to Zabajkalsk, but there was a problem with visa date - I came too early so they returned me back to China. Can someone advise me how to move forward from Manzhouli/Zabajkalsk to Moscow? I'm stuck here. Bus, train, from where to where? Any help is appreciated. Thanks.

Regards, Bogomil